ML19261F246

Environ Rept 76-31/3L:on 760831,low Reactor Coolant Pressure Trip Setpoints Less Conservative than Tech Specs.Caused by Minor Calibr Drift of Trip Setpoints

ML19261F246
Person / Time
Site:	Three Mile Island
Issue date:	09/30/1976
From:	Arnold R METROPOLITAN EDISON CO.
To:
References
GQL-1374, NUDOCS 7910250671
Download: ML19261F246 (3)

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3L, ON 8-31-76, CONCERNING LOW REACTOR COOLANT PRESSURE TRIP SETPOINTS BEING OUT OF SPECIFICA EION...D0 hT0T REMOVE

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Dear Sir:

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Decket No. 50-289 operating License IiO. DPR-50 In accordance. with the Technical Specifications of cur Three Mile Island I;uclear Station Unit 1 (TMI-1), we are reporting the fclleving repcrtable cccurrence:

(1) Report Number: IR 76-31/3L (2a) Required Report Date: September 30, 1976 (2b) Date of Occurrence: August 31, 1976 (3) Facility: Three Mile Island Nuclear Station - Unit 1 (h) Identification of Occurrence:

Title:

Lev Reacter Coclant Pressure Trip Secpcints Cut cf Specification Type: A repertable occurrence as defined by Technical Specifi-caticn 6.9.2.3.(1) in that the icy reacter ecclant pressure trip setpcints were fcund to be less conservative than those established by Table 2.3-1 of the Technical Specifications.

(5) Conditions Prior to Occurrence:

Fever: Core: 1005 Elec.: 83!i Mv (Gross)

RC Flev: ak0 x 100 lbs/hr.

RC Pressure: 2155 psig RC Temperature: 579C F FRZR Level: 225 inches FRa,R Temperature: 650C F 1481 242 D252

- September 30, 1976 Mr. J. P. i de' ' GQL 137h

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(6) Description of Cccurrence:

On August 31, 1976, while checking the reactor coolant pressure transmitters and corresponding trip setpoints due to noted differences in indication between the associated Beacter Protection System (EPS) channels , the low reactor ecolant pressure trip setpoints were found to be less conservative than these listed in Table 2.3-1 of the Technical Specification. The cbserved cetpoints were:

RPS Channel Table 2.3-1 Trip Actual Trip Settcint (tsic) Settcint (tsic) 3 1800 1795 C 1800 1787 I==ediately, the cut of specification pressure transmitters vere recalibrated and tested. The affected EPS channels trip set-points were verified as being within Technical Specifications limits. In addition, the pressure trip setpoints for the remaining EPS channels were tested and verified as being within Technical Specification limits.

(.7 ) Designation of Apparent Cause of Occurrence:

The cause of this cecurrence has been determined to be material in that the cut of specificaticn trip setpoints were due to miner calbiration drift in the associated Reactor Ccolant Syste=

pressure transmitters.

(8) Analysis of Occurrence:

It has been determined that this cecurrence did not constitute a threat to the health and safety of the public in that:

a. The maximum setpoint errer (13 psi) was less than the 30 psi instrument errer assumed in the unit's safety analysis,

b. The setpcints for the remaining two RPS channels were within Technical Specifications li=its.

(9) Corrective Action:

In additicn to the i==ediate corrective action described above, the possible installation of a te=perature cc=pensation circuit for transmitters to minimize drift frc= temperature changes is being investigated. Further, a prcpcsed change to the Technical Specifications which will take into acccunt the 30 psi instrument error assumed in the safety analysis is currently under review.

(10) Failure Data:

Transmitter Applicaticn: Reactor Ccolant Syste=, Narrev Range Pressur' Manufac'urer: Westinghcuse Electric Corporation.

Mcdel:  ;) FH Cther Applications in Plant: Ncne Similar Occurrences: A0 Th-2h, A0 75-15, A0 75-26 6'ncergly, .

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1481 243 R. C. Arnold Vice President 3CA:JMC:kl